148 Transactions of the Society. 



matised in 1886, since when there has been no further improve- 

 ment ; others, better acquainted with practical optics, have predicted 

 that owing to the instability of these new fancy glasses there would 

 be a falling off in the performance of the finest kinds of object- 

 glasses, because manufacturers would only use glass well proved 

 for its stability, the optical qualities of which conform more nearly 

 to the ordinary old-fashioned flints and crowns : but this observa- 

 tion of the tertiaries of Coscinodiscus aster omphal us in a balsam 

 mount has proved the fallacy of both these statements. 



This apochromatic ^ is more sensitive to tube-length, stands a 

 larger axial cone, bears a deeper eye-piece, and has sharper definiton 

 than any Microscope lens I have as yet seen. 



